High speed packet access (HSPA) evolution refers to the third generation partnership project (3GPP) radio access technology evolution of high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA). Some of the major goals of HSPA evolution include higher data rates, higher system capacity and coverage, enhanced support for packet services, reduced latency, reduced operator costs and backward compatibility.
It has been agreed that an enhanced high speed medium access control (MAC-ehs) entity is extended to include a function for segmentation and multiplexing from different priority queues in addition to being able to receive radio link control (RLC) protocol data units (PDUs) of flexible size. The addition of new MAC-hs functionalities requires modification to the conventional MAC-hs architecture.
FIG. 1 shows a universal terrestrial radio access network (UTRAN) side MAC-ehs entity 100 proposed for HSPA evolution. In the proposed MAC-ehs architecture, segmentation is performed per logical channel by segmentation entities 112. The segmented MAC-ehs service data units (SDUs) are then multiplexed by the logical channel identity (LCH-ID) multiplexing entities 114 based on the logical channel identity, and buffered in the configured priority queue 116. A MAC-ehs protocol data unit (PDU) is then generated from the MAC-ehs SDUs stored in the priority queue 116 and transmitted via a hybrid automatic repeat request (HARQ) entity 120.
FIG. 2 shows a user equipment (UE) side MAC-ehs entity 200 proposed for HSPA evolution. The received MAC-ehs PDU via an HARQ entity 202 is disassembled into reordering PDUs by the disassembly entity 204. The reordering PDUs are distributed to a reordering queue 208 by the reordering queue distribution entity 206 based on the received logical channel identifier. The reordering PDUs are reorganized according to the transmission sequence number (TSN). Reordering PDUs with consecutive TSNs are delivered to a higher layer upon reception. A timer mechanism determines delivery of non-consecutive data blocks to higher layers. There is one reordering entity 208 for each priority class. An LCH-ID demultiplexing entity 210 routes the reordered reordering PDUs to a reassembly entity 212 based on the logical channel identifier. The reassembly entity 212 reassembles segmented MAC-ehs SDUs to original MAC-ehs SDUs and forwards the MAC-ehs SDUs to upper layers.
The proposed MAC-ehs entity 100 for the UTRAN-side performs segmentation on a per logical channel basis. However, the segmentation of the MAC-d PDUs should not be performed at that level, since the packet will not be transmitted immediately. The multiplexed reordering PDUs are buffered in the priority queue 116 and sent at a later time. Segmentation of the MAC-ehs SDUs prior to knowing the exact channel conditions is inefficient. The segmentation should not be performed prior to the time interval in which the packets will be transmitted. It would be desirable that the segmentation be performed at the time when the MAC-ehs PDU is created and the size of the transport block (TB) for that transmission time interval (TTI) is known. In addition, if the UTRAN is updated to segment the MAC-ehs SDUs right before the MAC-ehs SDUs are sent, the WTRU must also be updated accordingly.
In the proposed MAC-ehs entity 200 in FIG. 2, the LCH-ID de-multiplexing entity 210 routes the MAC-ehs segments to the reassembly entity 212 based on the logical channel identity. This requires reassembly entities for different logical channels within the same queue. In addition, if MAC-ehs headers are optimized, the system information (SI) field will not be present for every logical channel, but it will be present only for the priority queue.